Offshore marine platforms are often constructed for the purpose of producing oil and/or gas from a formation below a seabed. These offshore marine platforms typically employ an undersea structure referred to as a “jacket”. Patents have issued that are directed to platform jackets. One example is U.S. Pat. No. 4,721,416 entitled “Submersible Offshore Drilling and Production Platform Jacket” issued to Garcia. U.S. Pat. No. 4,721,416 is incorporated herein by reference.
Patents have issued that relate to the disposal of jackets. An example is U.S. Pat. No. 6,354,765 entitled “Method of Transporting and Disposing of an Offshore Platform Jacket” issued to Jones. U.S. Pat. No. 6,354,765 is incorporated herein by reference.
After the useful life of a marine platform is over, the platform and the jacket must be removed so that they are not a hazard to navigation. Because portions of a marine jacket can extend into the seabed (for example, see FIG. 1 of U.S. Pat. No. 4,721,416, part of the jacket (sometimes referred to as a jacket leg) must be removed below the mud line. It is important to remove jacket legs below the mud line because they are a hazard to navigation. They are also a hazard to fishing boats that employ nets, such as shrimp boats.
A caisson can be one of several columns made of steel or concrete that serve as the foundation for a rigid offshore platform rig, such as the concrete gravity platform rig. A caisson can also be a steel or concrete chamber that surrounds equipment below the waterline of a submersible rig, which can protect such equipment from damage.
Prior art methods of removal of caisson/jacket legs below the mud line have included digging a trench around the exterior of the caisson/jacket leg and, after such trench has been dug, cutting the caisson/jacket leg. This prior method has the disadvantage of requiring the extra step of digging the trench, dealing with the materials removed when digging the trench, along with maintaining the stability of such trench during cutting of the caisson/jacket leg. If stability of the trench is not maintained, the trench can collapse during cutting operations risking bodily injury along with damage to equipment.